The increase in the population, respectively the consumption of food and energy resources for its existence, is also connected with the ever-increasing demands on modern technologies in terms of ecology. Bulgaria has significant untapped potential from renewable energy sources (RES). Biomass moisture is an important controllable factor. The article reflects a mass loss study for drying low-grade wood. The subject of the study is a technology for using low quality wood as a raw material for heat generation. Attempts show that the energy for drying is roughly the same, but the construction of the particular machine does not allow the use of more powerful burners as the machine efficiency will deteriorate due to insufficient area of the heat exchanger.